The present invention relates to apparatus for recording and reproducing video signals on and from a magnetic tape whose traveling speed can be selectably changed. More particularly, the invention relates to an apparatus for recording and reproducing video signals on and from a magnetic tape which is traveling at a speed in accordance with a mode selected from between a long-time recording and reproducing mode and a short-time recording and reproducing mode.
The conventional video signal recording and reproducing system, ordinarily, forms tracks on a recording tape in a manner which leaves an unrecorded zone or band called a guard band between neighboring tracks in order to prevent the generation of beats between the signals of neighboring tracks due to tracking deviation of the head at the time of reproduction. However, in the above mentioned system, since unrecorded bands are provided between tracks, the utilization efficiency of the tape has been poor.
Accordingly, the assignee of the present invention has previously developed a system wherein tracks are formed on a tape without gaps or guard bands between neighboring tracks. Moreover, a color video signal can be recorded and reproduced on such a tape without the occurrence of interference beat disturbance. This system is described in U.S. patent application Ser. No. 731,935 entitled "Color video signal recording and/or reproducing system" filed Oct. 13, 1976, now U.S. Pat. No. 4,178,606 and assigned to the assignee of this application. In this previously developed system, a pair of azimuth heads have gaps which are inclined at a certain azimuth angle, in opposite directions from a line perpendicular to the longitudinal direction of the track. Neighboring tracks are formed in contiguous contact side-by-side without a gap or guard band therebetween. The phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period. The direction of this phase shifting is reversed from one track to the next. In accordance with this system, the tape utilization efficiency is high since the tracks are in close proximity to each other. Moreover, there is no beat disturbance.
On the one hand, in apparatuses for recording and reproducing video signals, the accompanying audio signal is generally recorded by a stationary head. For this reason, as the traveling speed of the magnetic tape is increased, the recording and reproducing characteristics and S/N ratio of the audio signal are improved, and, in addition, noise due to wow and flutter of the magnetic tape becomes relatively less. On the other hand, as the traveling speed of the magnetic tape is increased, the recording and reproducing time for the same length of the magnetic tape becomes shorter.
Accordingly, a video signal recording and reproducing apparatus which can be selectively operated, according to the purpose of use, in a shorttime recording and reproducing mode having a high magnetic tape traveling speed and a long-time recording and reproducing mode having a low magnetic tape traveling speed has been reduced to practice in a concrete form. Since recording and reproducing are carried out with the tape driven at a high speed in the shorttime recording and reproducing mode, the recording and reproducing time is short for the same tape length, but the audio signal is recorded and reproduced with good characteristics. In the long-time recording and reproducing mode, although the characteristics of the audio signal are somewhat inferior to those in the case of the short-time recording and reproducing mode, recording and reproducing of the video signal and the audio signal for an even longer period can be carried out.
In a video signal recording and reproducing apparatus of this heretofore known kind, however, the track width of the magnetic head, the traveling speed of the magnetic tape and other values are so set that the tracks are formed without gaps therebetween in the long-time recording and reproducing mode. For this reason, in the short-time recording and reproducing mode, gaps are formed between adjacent tracks, whereby guard bands are substantially formed, as described more fully hereinafter in conjunction with a drawing. As a disadvantageous consequence, the utilization of the tape at the time of this short-period recording and reproducing mode has been poor.